Fluvial response to climate and sea-level change: implications from the Skeleton Coast, Namibia.
Date
2005
Authors
Krapf, Carmen Barbara Elke
Stollhofen, H.
Werner, Mario
Editors
Advisors
Journal Title
Journal ISSN
Volume Title
Type:
Conference paper
Citation
8th International Conference on Fluvial Sedimentology, 7-12 August, 2005: pp. 166.
Statement of Responsibility
Krapf, C.B.E. Stollhofen, H. and Werner, M.
Conference Name
International Conference on Fluvial Sedimentology (8th : 2005 : Delft, The Netherlands)
Abstract
The Cenozoic climate of southern Africa has been a subject to influences of both global and regional nature. Orbitally controlled cycles, stepwise global coolings, the
evolution of the ocean current system and differential uplift have dominantly influenced the climate history during the last 65 million years. The interplay between
these factors has been complex, and the resulting climatic history is known only in a
very broad outline for most of the Early Cenozoic. More is understood of Neogene
climates because of the better preservation of terrestrial proxy data, but it is only over
the last two glacial cycles that sufficient palaeoclimatic data have been assembled to
allow a tentative picture of the regional patterns of change to be drawn. Data sets of
oxygen isotope records from ocean sediment cores taken off the KwaZulu-Natal coast
show that the climate of the southern African subcontinent has oscillated in a manner
similar to that over much of the globe during the Middle and Late Pleistocene. Glacial
and interglacial conditions occurred with a quasi-periodicity of about 100,000 years in
response to Milankovitch forcing due to changes in the eccentricity of the earth’s
orbit. The period from 125.000-16.000 BP was characterized in high latitudes by a
series of pronounced rapid warmings, followed by slow variable declines to
progressively lower minima, as the deuterium isotopic record from the Antarctic
Vostok ice core illustrates. Proxy data sets show that similar variations occurred
throughout southern Africa.
However, a chronostratigraphic control on marine and continental Cenozoic deposits
for the Namib Desert, especially for its northern part, is largely missing. Most data
derived from continental deposits distributed across the Namib Desert and adjacent
areas. But there is a lack of sedimentological and chronostratigraphical data from
deposits of the mouth areas of the ephemeral river systems and from adjacent marine
terraces.
The Skeleton Coast in NW Namibia hosts a number of superbly exposed Cenozoic
sedimentary successions, which provide a unique insight into the Cenozoic
stratigraphy along the southwest African coastline. These deposits record the interplay
of marine, fluvial and aeolian processes and therefore represent prime research objects
to study fluvial response to sea-level and climate change. Along the incised banks of
the ephemeral rivers and especially the wave cut seacliffs several fluvially dominated
unconformity bounded sequences are exposed. Some of the rivers have built up
braided river dominated fans on the coastal plain, e.g. the Koigab River. Pleistocene
beach deposits form intermittent strips and ridges trending more or less parallel to the
coast representing elevated shorelines. They consist of largely unlithified marine sand,
gravel and boulder beds which attain thickness of up to 10 m. They are distributed
along the coast to the north of the river outlets due to the extreme wave and wind
action associated with the strong north trending Benguela Current. The elevations of
these coastal terraces range from +2 to +35 m asl. and are located up to at least 5 km
inland and reflecting eustatic highstands during the Late Tertiary to Quaternary.
School/Discipline
Australian School of Petroleum